Inducible Smooth Muscle‐Specific Knockout of Acid Sensing Ion Channel 1 Protects Against Pulmonary Hypertension

Abstract

Acid‐sensing ion channel 1 (ASIC1) is a proton‐gated cation channel that conducts both Na+ and Ca2+. ASIC1 is expressed in multiple cell types including vascular smooth muscle cells (SMCs) and endothelial cells (ECs). Our laboratory has previously shown that ASIC1 contributes to pulmonary arterial constriction and the development of chronic hypoxia (CH)‐induced pulmonary hypertension. However, the contribution of SMC versus EC ASIC1 to CH‐induced pulmonary hypertension is unknown. We tested the hypothesis that SMC expression of ASIC1 contributes to pulmonary hypertension and vascular remodeling by examining the development of CH‐induced pulmonary hypertension (barometric pressure of 380 mmHg for 6 weeks) in inducible SMC‐specific ASIC1 knockout (SMC‐Asic1‐/‐) and EC‐specific ASIC1 knockout (EC‐Asic1‐/‐) mice. The SMC‐Asic1‐/‐animals were used to examine the prevention and reversal of pulmonary hypertension by either inducing Asic1 knockout before CH exposure or following the establishment of pulmonary hypertension (3 weeks post‐CH). Pulmonary hypertension was assessed by direct cardiac puncture in anesthetized mice to measure right ventricular systolic pressure. Similar to global ASIC1 knockout (Asic1‐/‐) mice, SMC‐Asic1‐/‐ mice were protected from the development of CH‐induced pulmonary hypertension. In contrast, EC‐Asic1‐/‐ mice developed pulmonary hypertension comparable to wildtype Asic1+/+ mice (Figure 1). Furthermore, CH‐induced pulmonary hypertension was reversed by induction of SMC‐specific ASIC1 knockout following established pulmonary hypertension. CH‐induced vascular remodeling was assessed using smooth muscle α‐actin immunofluorescence to determine the medial thickness of small pulmonary arteries. The degree of arterial muscularization was significantly attenuated and/or reversed in SMC‐Asic1‐/‐ arteries (P<0.05). These findings were additionally supported by decreased CH‐induced proliferation (P<0.05) and migration (P<0.05) of pulmonary arterial SMC from Asic1‐/‐ mice, assessed by flow cytometry of BrdU positive cells and transwell migration assay, respectively. Together these data demonstrate that SMC, but not EC, ASIC1 contributes to CH‐induced pulmonary hypertension and vascular remodeling. Furthermore, these studies provide evidence for the therapeutic potential of ASIC1 inhibition to reverse pulmonary hypertension.